The invention relates to a steering control device for a vehicle, comprising a steering actuating means, such as a steering wheel, a pair of steerable wheels attached to the same wheel axle, means for transmitting steering impulses between the steering actuating means and the steerable wheels. The position of the steering actuating means is detected by a sensor means arranged in connection with the steering actuating means or the wheels, in order to generate a position signal proportional the steered angle of the wheels. The control device is connected to an electronic control unit for a vehicle brake control system, which system is arranged to brake the inside wheel when the position signal from the sensor means exceeds a predetermined value, in order to reduce the turning radius of the vehicle.
A common problem for front wheel drive cars having relatively large engines and/or wide tires, is a comparatively large turning circle. The problem may be worsened by other factors, such as a transversely mounted engines, a long wheelbase and impact absorbing beams, all combining to limit the available space for turning the front wheels.
Making the car body wider to accommodate the wheels is not always a possible solution, due to a combination of legal restrictions, practical reasons and the maximum width which would be accepted by consumers.
Known solutions to this problem involves making physical changes to the vehicle suspension, in order to temporarily or permanently move the pivot point for the steerable wheels towards the center of the turning radius, or cornering center. However, such a suspension arrangement optimized for a small minimum turning radius could, for instance, move the contact surface of the tire from the inner/center part to the outer part of the tire. A weight distribution of this kind would almost certainly have a negative effect on the handling of the vehicle at speed. Physically moving the pivot point, for instance by rebuilding the suspension so that the struts, rods and arms are attached to the wheel mounting inside the outer profile of the rim, may cause problems with the positioning and size of the brake calipers and the cooling of the brake discs, etc.
A further solution is to make all four wheels steerable, so that the rear wheels are turned in the opposite direction to the front wheels at low velocities. Although this has been tried and is practically possible, such systems are complex and add to the cost and total weight of the vehicle.
For multi-wheel or tracked vehicles the problem is simply solved by locking all wheels on one side of the vehicle. This would not be a possible solution for vehicles such as an automobile, as the tire wear would be excessive on tarmac or concrete surfaces.
According to one embodiment of the invention, the steering control device for a vehicle, comprises a steering actuating means, such as a steering wheel, a pair of steerable wheels attached to an axle, means for transmitting steering impulses between the steering actuating means and the steerable wheels. A sensor is arranged to detect at least one parameter relating to a condition of the steering actuator and generate a signal indicative of said condition, which signal also categorizes each of the steerable wheels as an inside and an outside wheel respectively. One condition detected by the sensor may be the position of the steering actuating means, in order to generate a position signal proportional the steered angle of the wheels. The control device also includes an electronic control unit for a vehicle brake control system, which system is arranged to brake the inside wheel when the -position signal from the sensor means exceeds a predetermined value, in order to reduce the turning radius of the vehicle.
The brake control system is actuated as the steering actuating means is approaching or actually reaches its end position. This usually occurs when the vehicle is stationary or is being turned at a relatively low speed, with the steering wheel turned to or near its limit position. However, it is also possible to prevent the system from operating if the vehicle velocity exceeds a predetermined value. In this way the braking action will only take place if the vehicle velocity is less than e.g. 10 km/h, preferably less than 7 km/h.
A further condition that can be detected by the sensor is the rate of turning of the steering means or actuator. For instance, in an emergency situation a driver may need to swerve suddenly to avoid an obstacle on the road. Such a sudden turning of the steering actuator is detected by the sensor and the inside wheel is braked briefly, in order to assist the driver in avoiding said obstacle. As an operation of this type usually involves turning the wheel in a first direction, to avoid an obstacle, and then in a second direction, to move the vehicle back to its original path, the steered wheels will be braked alternately. As this condition can occur at speeds higher than the velocities stated above, it is important that the brakes are only actuated for a short time and that a vehicle stability system, or a similar system can override this function.
In addition to a standard steering wheel, the above-mentioned steering actuating means can also be electrically controlled e.g. by a joystick or a system of push buttons. The steering transmitting means can either be a standard mechanical steering linkage or an electrically or electronically operated steering system also termed xe2x80x9csteer-by-wirexe2x80x9d.
The steering control device also comprises an electronic control unit for the brake control system of the vehicle. This electronic control unit is of a type, which is provided in most modern vehicles and can be part of an anti-locking brake system a vehicle traction system or a vehicle stability control system. Common for all these systems is that they can control the vehicle brakes independently of the driver actuated control system, and that they prevent the wheels from locking during actuation of the brakes. The exact type of anti-locking control system used is, however, not relevant for the invention.
The invention also relates to a method for operating a steering control device as described above. As the steering actuating means approaches or reaches its end position, a signal is sent from the position sensor indicating that the driver requires the vehicle to turn sharply. The position signal is transmitted to the control device, which in turn transmits a signal to the electronic control unit for the vehicle brake control system. The brakes will then be actuated in such a way that the inside wheel is braked. The braking action causes a virtual displacement of the turning center of the inside wheel and reduces the turning radius of the vehicle.